The present invention relates to electroacoustic transducer and, in particular, to transducers of the type utilizing piezoelectric bender members as active transducer elements.
Bender-type piezoelectric or piezoceramic transducers are rather well known and have been used to advantage in a variety of forms. One such type is provided by the use of a circular, piezoelectric disc that is securely bonded to a circular metal plate so as to vibrate in an umbrella-like mode when mechanically or electrically energized. Such discs, however, have limited power capabilities. Also, because they are disc-shaped, a maximum packing density is not easily achieved. Compared with square or rectangular configurations having sides equal to the disc diameter, considerably less exposed surface area is formed of piezoelectrically active material.
Another type of bender transducer utilizes a square or rectangular piezoelectrical bender in the form of a single, solid plate. Such a geometry clearly is more favorable, but the use of the single plate still results in the umbrella-like vibratory motion of the disc configuration. Since the piezoelectric coupling is in all directions, all edges move and, to produce the umbrella motion, they require support at their corners. The need for this support presents significant constructional difficulties and further reduces the strength of the transducer element when subjected to pressure loads across its surface.
The present invention has as one of its objects the provision of a bender transducer which is capable of utilizing the square or rectangular bender configuration to facilitate construction and provide greater structural strength.
Another important object is to provide a transducer element structure that results in relatively higher electroacoustical efficiencies due, particularly, to the nature of its piezoelectric coupling.
In a manner to be described, the objects of the invention are achieved by using elongate, thin and narrow, piezoelectric bars or strips. The strips extend lengthwise of a flexible support plate to which they are securely bonded in a tightly-compacted side-by-side arrangement. The plate itself is rigidly engaged and supported at its longitudinal ends. Consequently, forces tending to cause the piezoelectric bars to lengthen or shorten result in a bending or flexing of the bars and, of course, the end-restricted plate to which the bars are bonded. To energize the bars and transduce electroacoustical signals, a circuit is coupled across each bar so that, in effect, the bars become a plurality of parallel capacitors. In a preferred form, the strips or bars are bonded to both sides of the plate although a single sided arrangement is operable. To improve flexibility, the plate itself can be hinged in a manner which will be described.